The Impact of Rock Climbing Disturbance on on Cliff commun

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Georgia R Harrison - Thesis Seminar, March 2020 Appalachian State University.

Abstract: Cliff communities are dominated by stress-tolerant, often cryptic lichens, bryophytes, and vascular plants whose abundance is controlled by harsh abiotic conditions. These taxa vary in their requirement for soil substrate, water, and sunlight and ability to withstand disturbance. Rock climbing is a major source of anthropogenic disturbance to cliff ecosystems. To assess the impact of climbing and habitat variability, climbed and unclimbed areas at Table Rock and Hawksbill Mountain in the Linville Gorge Wilderness area in North Carolina were surveyed for lichens, bryophytes, and vascular plants across 39 vertical transects.
I observed 42 lichen, 21 bryophyte, and 22 vascular plant species. Canoparmelia alabamensis was a new record for the state of North Carolina while 21 other species (17 lichens, four bryophytes) were Burke County records. Linear models indicated species richness and diversity were most strongly related to ledge and crack surface area for all three taxonomic groups. Climbed plots were less diverse and less species rich than their unclimbed counterparts at Table Rock. Climbing impacted lichen growth forms differently, causing decreased foliose and fruticose cover, and increased crustose cover. Climbing impacts cliffs by holding back ecological succession to the pioneer stage, with abundant crustose lichens, while removing larger, later successional stage lichens. Soil development, a critical step in vascular plant establishment, is also hindered. Since cliff vegetation varies by site due to differences in surface heterogeneity, each potential climbing area should be surveyed, especially for cryptic species, before management decisions are made. Since unclimbed cliffs were the most species rich and diverse, it should be a priority for these areas to remain undisturbed.
Surface heterogeneity is an important habitat variable for cliff ecosystems, but has not been consistently measured. Structure-from-Motion (SfM) techniques could afford a standardized method for measuring surface heterogeneity. We used color photographs and SfM to create 3D models of cliff faces that were surveyed for vegetation. Surface heterogeneity was calculated as average, standard deviation, and coefficient of variation of each plots’ average elevation, Terrain Ruggedness Index (TRI), Topographic Position Index (TPI), and roughness at four different focal statistic neighborhood sizes. Roughness and average elevation at larger neighborhood cell sizes weakly correlated with all features and crevice surface area. Vascular plant richness and diversity were correlated with a few measures of remotely modeled surface heterogeneity. The methodology developed in this study will help lay the ground-work for developing a novel technique to quantify structural spatial variability on cliff faces, which could lead to an increase in measurement consistency among cliff ecology researchers.

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